Before Kay Segler leaves BMWís M GmbH performance division to once again head the Mini brand, he has opened the vault to show a number of rarely or never seen concept cars and proposals from the divisionís rich 25-year history. We were able to take a close look at the vehicles and quiz engineers and executives about the thinking behind these cars and why they didnít make production. (The current-gen M3 pickup that debuted last week, is sure to join this collection one day, too.)